The present invention relates to a scanning pattern drawing apparatus. More particularly, the present invention relates to a scanning pattern drawing apparatus which scans the surface of a workpiece with a beam of light from a beam issuing device so that a pattern is described on the workpiece with the issued light beam being controlled on the basis of pattern drawing data stored in a pattern memory.
Scanning pattern drawing apparatuses are conventionally used to draw patterns on workpieces such as liquid-crystal electrodes and shadow masks. As shown schematically in FIG. 9, a conventional scanning pattern drawing apparatus is composed basically of a laser light beam generating unit 203 which issues laser light 201 toward a shutter unit 202, a scanning unit 205 which scans the surface of a substrate (workpiece) 204 such as a shadow mask with laser light 201 passing through the shutter unit 202, a memory 206 for storing pattern drawing data, and a controller 207 for reading data from the memory 206 and for controlling the scanning unit 205.
The controller 207 outputs timing pulses in response to scanning by the unit 205 with laser light 201 so that pattern drawing data is read from the memory 206. On the basis of the output data, the shutter unit 202 is turned on and off so that the substrate 204 is exposed to the laser light 201 in such a way that a predetermined pattern is described in accordance with the pattern drawing data.
Considering one period of scanning with laser light, the number of pieces of data read from the memory 206 is the same as the number of timing pulses produced by the controller 207.
With the recent demand for liquid-crystal panels capable of producing higher image quality or for integrated circuits having a higher packing density, it has been required that finer patterns be described on liquid-crystal electrodes or shadow masks. To meet this requirement and draw the finest possible patterns, manufacturers have generally taken two approaches. The first approach involves producing finer dots by minimizing the spot size of the laser beam, and the second is to increase the number of pixels in the pattern by maximizing the density of dots.
However, the number of pieces of data that are to be stored in memory increases with the number of pixels, so that the frequency of timing pulses for reading the data has to be increased as the number of pixels increases. At higher frequencies, it becomes difficult to control the timing pulses, and serious problems arise such as the generation of interfering electric waves.